So what would happen if the current ruling on who was and wasn't a dual citizen applied to all of our former prime ministers?

And would any elected after 1949 —when Australian citizenship was created — run into any trouble today?

So, would it be an issue if all of our former PMs were under the same rules as today?

In short?

Yep.

UNSW Law Dean George Williams said it would be a problem for a number of former PMs.

"The answer is today that this would be a problem for any parliamentarian or prime minister where they hold the dual citizenship of another nation. So yes, a number could well be in difficulty," Professor Williams said.

"This may not have always been the case at the time though, especially prior to the creation of Australian citizenship in 1949.

"Before then, Australians were British subjects, status shared with other nations, meaning that the same difficulties did not arise for people from nations such as the United Kingdom, New Zealand and Canada," Professor Williams said.